unable to get any thing on screen

what happens is i turn on my computer fan starts the green light comes on the monitor then it turns red then just a blank screen i have tried another signal cable without success i have an onboard graphics card any ideas would be grateful

Hi northumbria61,
thank you for your reply but every thing is back to normal,
as before i removed all cables removed memory sticks i have a hand held computer vaccum cleaner so i clean all the inside which was not very dirty put it all back and hey presto every thing works as i am on my desk top now.
Once again many thanks
kalbert27